Electrolytic process of obtaining metals from their fused compounds.



UNITED STATES PATENT OFFICE.

GEORGE I. SOHOLL, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO CHARLES W. ROEPPER, OF SAME PLACE.

ELECTROLYTIC PROCESS OF OBTAINING METALS FROM THEIR FUSED COMPOUNDS.

SPECIFICATION formingpart of Letters Patent No. 679,997, dated August 6, 1901.

Application filed November 14,1898. 1

To all whom it may concern: I

Be it known that I, GEORGE P. SOHOLL, a subject of the Emperor of Germany, residing in Philadelphia, in the State of Pennsylvania, have invented certain new and useful Improvements in Electrolytic Processes for Obtaining Metals from Their Fused Compounds, whereof the following is a specification.

In the various processes which havehitherto been invented and used for the purpose of electrolytically deriving metals from their fused compounds the use of metallic sulfid as the compound to be decomposed electrolytically in its fused state has been avoided by reason of the exceedingly high fusing-point of sulfids as a class. Thus, for example, sodium sullid is fusible only at a temperature much above the point at which metallic sodium vaporizes. Its use, therefore, in the electrolytic production of metallic sodium is difficult.

I have discovered that by using an initial proportion of sulfid in combination with a more fusible compound of the same metal a fusible electrolytic bath may be prepared without unduly increasing the temperature requisite for fusion, and in this way Iam enabled to take advantage of the very low electromotive force required for the decomposition of a bath containing a sultid. Furthermore, by continuously renewing the non sulfur component of the bath I find that this-ad vantage may be maintained continuously,

little if any more of the comparatively expensive sulfid being needed.

In order to carryout this process, it is only necessary to choose for the non-sulfur component of the bath a comparatively fusible compound of the metal desired, which is easily convertible into 'asulfid by the sulfur generated at the anode by the electrolysis of the sulfid.

Briefly stated, therefore, my invention consists in the employment in the electrolytic production of metal by fused-bath electrolysis of an electrolyte composed of a mixture of a sulfid and another more fusible compound of the metal desired, which is easily conyertible into a sulfid by nascent sulfur.

I will describe my invention as I practice it in the production of metallic sodium, pre- Serial No. 696,454 (No specimens.)

mising that it is applicable under the conditions which have just been stated to the production of other metals and that the specific mention'of sodium is typical and not restrictive.

I prepare an electrolytic bath composed of about equal parts of sodium sulfid and caustic soda. Although the meltingpoint of so dium sulfid is, as has been stated, high, the melting-point of this combination is not very much above that of caustic soda. The bath having been heated to fusion, I then pass an electric current bet-ween suitable anodes through the fused electrolyte. By reason of the presence of the sulfid a very much lower voltage may be used than would be required if caustic soda alone were used. The theoretical voltage of the decomposition of sodium sulfid is one and eight-tenths volts; but I have been able to elfect the decomposition of my electrolyte when the voltage absorbed in decomposition is considerably lower, going down as low as one and two-tenths volts, and sometimes even lower. I maintain the current at such a low voltage that the current decomposes the sulfid only, liberating the metallic element at the cathode, which is collected in the usual manner. Sulfur is liberated at the anode in. 3mm nascent, the cansticsodaimmediatelyconvertingitintosodium sultid. By continuously supplying caustic soda as fast as the sodium is produced at the cathode the proportion of sodium sulfid is kept constant, the process proceeding continuously, as has been described. In this way it will be observed that the electrolysis is to all intents and purposes the electrolysis of a suliid salt only, and yet a small initial quantity of the comparatively expensive sulfid is all that need be introduced, and this is rendered readily fusible by admixture with the other compound.

I have not yet been able to ascertain with certainty the reactions which take place; but they appear to be complicated by the presence of polysulfids.

I may here point out certain advantages which the process thus described presents over processes for obtaining metallic sodium by the electrolysis of caustic soda. These are the economic advantage of low-voltage ourrent and the absence of that very considerable element of danger in the caustic-soda process which results from the generation of hydrogen at the cathode. Owing to the heat at which the process is carried on the hydrogen so generated frequently explodes. To avoid this danger in such processes, very small plants have to be used. In my process there being less hydrogen liberated and that under a lower temperature, a single plant may be safely enlarged, 'so as to have a very great productive capacity with consequent economy of operation.

i In obtaining metals other than sodium other compounds than the hydroxids may be used as the non-sulfur component of the bath; but the choice of this component is clearly indicated by two conditions. It must be a comparatively fusible compound of the desired metal, and it must be one which is convertible into a sullid by nascent sulfur.

subjecting the fused bath to electrolysis by the action of suitable electrodes, substantially asdescribe'd. I

2. The process of obtaining metals by the electrolysis of their fused compounds, which consists in fusing a bath composed of a mixture of sulfid of the desired metal'w-ith a more fusible compound of said metal which is convertible into sulfid by nascent sulfur; and subjecting the fused bath to electrolysis by the action of suitable electrodes under a current which will decompose the sulfid only, substantially as described.

'3. The process of obtaining metals by the electrolysis of their fused compounds, which consists in fusing a bath composed of a mixture of sulfid of the desired metal with a more fusible compound of said metal which is convertible into sulfid by nascent sulfur; subjecting the fused bath to electrolysis by the action of suitable electrodes under a current which will decompose the sulfid only; and continuously renewing the bath by addition of the other constituents in proportion as the metal ingredient is liberated at the 

